Centrifugal compressor.



S. A. MOSS.

GBNTRIFUGAL COMPRESSOR.

APPLICATION FILED DEO.10, 1904.

. 1,075,300f Patented 001317, 1913.

2 SHEETS-SHEET l.

InOentol':

mane snares rhrnn'r enric I BAHFORKB A MOSS, F LYNN, NASSAGHU$MES, ABSIGNQR 'E'O GENERAL ELECTRIC GOMI'ANY, A CORPOBATEDN' 01? NEW YORK.

cnmalruoan ccnraassoa masses.

- To all whom it may concern Be it known that I, SAnnonn A. Moss, a

citizen of the United /States, residing ,at.

m1, county of Essex, State of 'Massac usetts, have invented certain new and.

useful Improvements 1n Gentrifugal Cornpressors, of which the following is a spanfication.

The present invention has for its ob ect t improve the efliciency and constructlon of centrifugal compressors, as will be more fully set forth hereinafter.

In carrying out my invention a compressor having one, two or morestages 1s provided. When it is desired to furnish air or other gas at relatively high pressure, the discharge conduit of one compressor or stage is connected to the inlet conduit of another compressor or stage, and so on. When it is desired to furnish compressed air or other gas at relatively low pressure but in relatively Large quantities, the stages of the compressor may be arranged to discharge in mult ple The rotary elements may all be mounted on th same or difi'erentshafts, and be driven by on or more sources of power. The construction of the compressors is similar except that the cross-sectional area of the-working passages, or passages between the blades in the first or low pressure compressor, is somewhat greater than that of the passage in the second or higher pressure compressor, the cross-sectional area of the passages in the succeeding compressors gradually decreasing as the pressure of the fluid increases. Each revolving element is mounted on a suitable shaft, supported in one or more hearings in the com ressor casing or on separate supports. T said element is provided with a number of radial vanes or blades sharpened ends arrangedto properly receive and discharge the fluid undergoing compression. As the element rotates, the air or other elastic fluid is discharged outwardly, due to centrifu al force. The blades or vanes mounted on t e impeller may be closed in at the sides by plat w h rotate therewith, or the walls of the stationary casing may he employed to complete the sides of the .airseonveying passages. When the'former arrangement is to keep down the leakage. The direction or fipeeifleation .of Letters Patent,

Application filed Ileeember 10, 1904. Serial K0. 286,373.

PatentedGcit. 7, 19M

angle of entrance of the air or gas o b compressed into the wheel or impeller is an important feature. The fluid should be de livered to the rotating blades or vanes in a plane at right angles, or substantially so, to the axis of rotatlon. To accomplish this, stationary directing vanes are employed which extend toward a common point at their receiving end, and at their discharge ends are situated in close proximityto t e receiving ends of the rotating blades. If the impeller speed is such that the pressure accruing through the conversion of velocity into pressure is less than twice the pressure at the periphery of the impeller, the nozzle re .uired to pr perly bring the air to rest will be holly d vergent, considered from the impeller outward. In this case the pressure variation is so slight that th spec fi volume does not change greatly. If however the impeller -speeds are very high, then the pressure due to the conversion of the velocity may be such that the pressure in the scroll or discharge conduit is more than twice the pressure at the periphery of the impeller. In such cases th nozzle, to properly bring the air to rest, must first converge and later diverge. This is due to the fact that in the anterior or converging portion of the nozzle th velocity does not decrease ery rapidly, while, on the contrary, the pressure increases rapidly. In order to take care vof the decrease in V ocity only, the nozzle should diverge, but owing to the fact that the increase in pressure is accompanied by a decrease in volume, provision must be made therefor by making the anterior portion of the nozzle converge. Tostate the matter in a difi'erentway, the velocity decrease so slowly compared to the reduction in volume due to the increase in pressure that theanterior portion of the nozzle mum gradually reduce in cross-sectional area. lnthe posterior ,or diverging portion of thenozzle the velocity decreases very rapidly, and in .order to make provision for this-the walls must diverge very rapidly. In this; portion therefore the contraction of'theair due to increase of pressure doesuot x rcise a very marked in- ,fiuence; Therefore,- in order to mak th proper provision for both the velocity action and the contraction action, the posterior portion of the nOZZlQ-llhllSt be wholly, divergent.

nozzlemay be divided by partitions .into sections or not as desired. Whether the nozzle is or is not divided into sections the separate streams of fluid delivered from the vane spaces will be received by it .and the velocity at once converted into pressure. It will be seen that the conversion from velocity to pressure takes place immediately after the maximum velocity is created instead of at some distant point,

which results in a loss in efliciency. When a compressor or a stage of a multi-stage compressor is intended to produce only a relatively small increase in pressure, it is unnecessary to provide the nozzle with converging walls on the receiving or anterior portion, but where higher pressures are to be produced it is necessary, in order to obtain the best results, to use them. This applies whether the nozzle is subdivided'into sections or not. Surrounding the .nozzle and formed in the casing, .or otherwise suitably supported and connected, is a scroll or discharge pipe which gradually increases in cross-sectional area to accommodate the increased amount of fluid due tothe amounts discharged by the vane spaces. The crosssectional area of the scroll pipe should be such as to retain the fluid in its compressed state.

In the accompanying-drawings, which illustrate certain embodiments of the invention, Figure 1 is a view in elevation of a centrifugal air compressor with certain of the parts broken away to show the-construction of the vanes and nozzle; Fig. 2 is a view taken at right angles to that of Fig. 1, with certain of the parts broken away to show the internal construction; Fig. 3 is a diagram representing the velocities of the fluid passing through the passages between the directing vanes, and also the velocity of the fluid passing through the vane spaces on the rotating element; Fig. 4 is a detail view of a packing employed between the rotating and stationary parts; Fig. 5 shows the in-' vention applied to a multi-stage compressor having two or more stages; Fig. 6 is a detail view of a nozzle having converging and diverging portions; Figs. 7 and 8 are diagrammatic views of impeller blades and velocity diagrams, and Fig. 9 is an enlarged view of the nozzle shown in Fig. 1.

The casing for the compressor is made up of two principal parts 1 and 2 which are flanged and secured together by the bolts 3.

4 represents the main shaft, which is supported in a suitable bearing 5 and carries the revolving element 6. The revolving element is keyed or otherwise secured to the shaft. Its hub is finished off true, and surrounding it is an adjustable packing 7 The rotating element is provided with a plurality of vanes 8, which may be curved at their ends and between said vanes are passages that diverge outwardly as shown. The

object in curving these vanes at the ends is to cause them to receive and discharge the air or other fluid at the most effective angle. The sides of the vanes are covered by plates or walls 9 and 10, Fig. 2, which serve to confine the fluid undergoing compression in the separate vane spaces. However I may omit these walls and have the vanes extend to the casing. The wall 9 forms a continuation of the supporting hub and it may or may not be formed integral therewith. The wall 10 may be formed integral with the "anes or be attached thereto with suitable bolts or other retaining devices. It is provided with an enlarged central opening, concentric with the axis of rotation, within which are located the directing vanes 11 and the shield 12. The shield is conical in form and, as shown, covers the end of the shaft and hub of the rotating element. The directing vanes 11, at. their receiving ends, form an angle of about 45 with the axis of rotation, while the discharge ends are parallel with the shaft and are surrounded by the inner ends of the blades on the rotating element. By means of this construction the incoming fluid is prevented from striking the rotating part of the wheel or impeller until it is delivered to the vanes 8, which, bytheir centrifugal action, simultaneously increase the velocity and pressure of the fluid. shown in Figs. 1 and 2, approximately onehalf of the pressure of the fluid discharged is due to the centrifugal action of the wheel itself, and the remainder to the action of the nozzle.

The vanes 11, the shield 12, andthe flange 13 of the part 2should be as smooth as possible in order to permit the air to freely enter the vane spaces. in the rotating element, and this without undue losses due to eddies, etc. To the flange 13 of the casing is bolted a flange 14 which receives the screw-threaded end of the conduit 15. The conduit 15 may be connected with any suitable source of supply, such as the atmosphere, a tank or the discharge end of another compressor.

I have found in actual practice that in some cases there is a tendency for the fluid passing through the vane spaces to leak between the wall 10 and the revolving element andthe casing, and reenter the vane spaces. If thi leakage is excessive, a packing may be employed, such as shown in Fig. 4, where-' in 16 represents a cylindrical extension of the casing to which the stationary directing 'vanes are attached, and 17 the hub-like portion on the right hand side, Fig. 2, of the rotating element. Between the parts 16 and 17 a chamber is formed to receive the soft packing 18, which is adjusted by means aces,

with cylindrical shoulders or grooves 20 to receive the nozzle 21. In the present instance the nozzle is shown as being provided with a plurality of sections'orassages. The nozzle should be provided wi h a throat or point of restriction 22 and diverging side walls 23. By reason of the divergence of the walls of the nozzle or of the sections of the nozzle, where such sections are employed, the velocity of the fluid received from the rotating element is converted into pressure. These passages extend tangentially or substantially so to the path of the outer ends of the moving vanes. The passages between the partitions should be relatively long with respect to their width so as to properly direct thefluid particles, and also to cause the fluid to be compressed as it, passes through them. By this I mean that the distance between the dotted line 410 of Fig. 9 and the dotted line 4:1 is much greater than the distance between the side Walls measured at any point in a plane perpendicular to the direction oi the flowofthe fluid. The portion42 of the nozzle between the sharpened inlet edges of the partitionsserves to collect or gather; the fluid particles preparatory to discharging them into the nozzle proper. The efiective action ot the nozzle in compressing the fluid, reducing its velocity to a negligible amount and increasing its temperature and density takes place in the nozzle between the dotted lines 4:0 and &1.

in Fig; 3, 24a of the larger diagram represents the absolute velocity 01? the airat the point oi? entrance to the nozzle with respect to earth; 25 the velocity 0% the wheel and 26 the relative velocity of the air passing through the wheel. Referring to the smaller diagram of Fig. 3, 2'1 represents the absolute velocityof' the fluid entering the wheel; 28 the velocity of the wheel atthe point of entrance and 29 the relative velocity of the air with respect to the vanes 8. The discharged by the nozzle or nozzle section is collected in the scroll pipe 30 which is formed in the casing. This scroll pipe gradually increases in cross-sectional area from one end to the other, and finally terminates in a flanged conduit 31, always, however, retaining the fluid in its compressed state.

Referring to Fig. 5, twoair compressors orstages 32 and 33 are shown, which are alike in all substantial respects. 32 repre sents the first or low pressure compressor, and 33 represents the second or higher pressure compressor. The comprmsor 32 recei'ves airor other fluid from the conduit in the same manner as is shown in Fig. 2. The fluid discharged theretrom is collected in the scroll pipe and is-discharged into the conduit 34, the latter being connected with the inlet of" the compressor 33'. Between each two compressors I may employ an; in-.

tercooler 35 0% suitable construction to I36- duce the temperature of the air or other gas undergoing compression. The present intercooler comprises a casing containing gas: carrying tubes, and pipes conveying a cool= ingfluid to and away irons the casing. I may employ a greater number of stages in the air compressors and between some or all of the stages intercoolers may be provided.

In Figs. 1 and 2 a nozzle is shown which is wholly divergent. This is suitable forcomparatively low impeller speeds. In order to have exactly the same nozzle action fiorgreat impeller speeds, a nozzle first convergent and then divergent should be substituted, as shown in Fig. 6. I therefore do,

not limit myself in this particular, and use that form of nozzle which} calculation and ex eriment show is best suited for each case. This nozzle is not provided with partitions as shown in Fig. 1, but they may be provided if desired. To state this matter in another way, I have found. that a compressible fluid discharged an impeller and compressed by certain amount due to centrifugal action, and at a certain temperature T due to this compression, and with a certain velocity V due to part of the energy in ut of im-.

peller can be tur-ther compresse by means of a stationary nozzle as already described, it the cross section of the stream is properly varied in the direction of flow of the fluid along it. ll have iound that there is a cer-. tain critical velocity, V which can be con. puted according tothe formula Yo V=Gritical velocity per sec. QIACCQlBKfllllOIl due to. gravity, ft. per sec.

per sec.

R Gxas constant in well known formula gar-:RT wherep is in lbs. per sq. it, v is in 7 cu. ft. per lb. and T is absolute Fahr. temperature.

==Ratio of specific heats at constant pressure. and constant volume.

.T Abs. Fahr. temperature at impeller 'exit.

In cases Where it is desirable to make the impeller exit velocity V in ft. per second greater than the criticalvelocity V as above computed: a nozzle isprovided which will conduct the stream so that its cross section is first gradually decreased until a point is reached where the velocity has been reduced to the critical velocity. There will be a certain amount of compression pron duced by the flow along the nozzle to this 9 point beyond that produced by the impeller. The nozzle is arranged so as to gradually increase the cross section of the stream beyond. this point. There is therebyproduced furthercompression. In cases where it is desirable to make the impeller exit velocity V infeet per second, less than the eritical velocity V, as above computed therois pros vided a nozzle which will conduct the stream so that its cross section is always gradually increased. This compresses the fluid beyond the amount accomplished by the impeller. In all cases it is assumed that the'impeller wheel receives the air at a point of comparatively small diameter and discharges it at a point of greater diameter. The exact ratio of diameters is not essential. By having the inner diameter of the Wheel at the point where the air is received of a greater or less ratio to the outer diameter, the relative degree of compression due to centrifugal action and to nozzle action is altered. I therefore do not limit myself to any particular ratio of diameters. The compression due to centrifugal action and nozzle action is also affected by the direction in which the vanes of the inlet guide are turned, and also by the direction in which the beginning and ending of the impeller vanes are turned. For instance, if the angles and velocity diagrams are as shown in Fig. 7, the absolute velocity V of the air in space upon leaving the impeller will be very great. On the contrary, if the angles are as indicated by Fig. 8, the velocity V of the air leaving the wheel will be much less. That is to say, the pressure combinations are possible. .the passages and vane angles may be so due to nozzle action will be much greater for the arrangement shown in Fig. 7 than for the arrangement shown in Fig. 8. In Figs. 7 and 8, W of the larger diagrams indicates the velocity of the impeller, V the absolute velocity of the air leaving the impeller, and R the velocity of the air relative to the impeller. The diflerence in the rela tive velocity indicated by V and R in the two figures is due to the curvature at the discharge ends of the vanes. In the smaller diagram, W indicates the velocity of the receiving ends of the impeller vanes relatively to the stationary guide vanes, V the absolute velocity of the air leaving the guide vanes and entering the impeller, and R the relative velocity of the air with respect to the guide vanes. The smaller diagrams in Fig7 and 8 represent the velocity of the air passing-through the directing vanes. Various relative effects can be secured by various other combinations of angles of the inlet guide and of the beginning and end of the impeller vanes, and I do not, therefore, limit myself in this particular. In Fig. 7 the velocity of the air relative to the impeller is shown to be the same at the entrance and exit. This is accomplished by having the total area of the passages by which the air leaves-the wheel somewhat smaller than the passages by which it enters, to make up for the contraction due to the increase in pressure from centrifugal action. However, other For instance In accordance with the provisions of the a patent statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof; but I desire to have it understood that the apparatus shown is only illustrative, and that the invention can be carried out in other ways. 5

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. In a centrifugal compressor for'elastic fluids, the combination of a casing, a rotating impeller mounted therein which is provided with radially disposed vanes having outwardly diverging passages between them, which vanes and passages confine the fluid and simultaneously impart velocity to the fluid and compress it by reducing its volume, directing vanes arranged to direct the incoming fluid against the inner ends of the impeller vanes, an annular nozzle located in the plane of the impeller which surrounds the outer ends of the vanes and is provided with tangential partitions and walls that decrease the velocity of the fluid to a predetermined small amount, and also further decrease the volume and increase its density before discharging it, and a conduit that surrounds the nozzle and receives fluid from it and retains the same in its compressed state. 2. In a centrifugal compressor, the combination of a rotating element which is provided with vanes shaped to simultaneously impart velocity to the fluid and compress it, directing vanes which direct the incoming fluid against the inner ends ofthe vanes on the rotating element in a direction per endicular to the axis of rotation, a shield w ich assists in directing the incoming fluid and prevents it from striking that portion of the wheel within the inner ends of'the vanes, a nozzle which surrounds the outer ends of the vanes and is provided with walls that decrease the velocity of and also the volume of the fluid and increase its density and temperature, and a discharge conduit which receives fluid directly from the nozzle and retains it in its compressed state.

3. In a centrifugal compressor for elastic fluid, the combination of an impeller which is provided with radial passages that gradually increase in cross-sectional'area toward the point of discharge and simultaneously impart velocity to the fluid and compress it,

novaeoo a casing for the impeller, an. annular nozzle that closely surrounds the impeller, is 10- oated in the lane thereof and receives the elastic fluid discharged by it, thin artitions compression 1S added to that due to the impeller, a conduit that surrounds the nozzle and receives the fluid from all of said passages and holds it in a compressed state, and a means for reducing the tendency of the fluid to cause eddies as it enters the impeller.

4. In a centrifugal compressor, the combination of arotary vane-carrying element, a casing therefor, means for directing the incoming fluid into the receiving ends of the vane spaces of the rotating element, an annular nozzle which surrounds the rotating element and is located in the plane of said element, straight walled partitions in the nozzle extending in the direction of flow of the fluid to form passages, each passage being provided with a restricted throat and posterior diverging walls which compress the fluid and reduce the velocity thereof and increase its density and temperature prior to discharging it, a plurality of means that cooperate with the rotary vanes. to direct the incoming fluid thereto, and a conduit which receives the fluid after it is discharged by the passages, at the same time preventing it from expanding.

5. In a centrifugal compressor, the comloination of a rotating element, vanes or blades thereon which extend radially and have their ends curved forward to dischargev the fluid with high velocity relative to the impeller, stationary vanes for directing the passage of fluid into the vane spaces of the. rotating element, which are alsocurved at the ends, the discharge ends of the directing vanes beingsurrounded bythe receiving ends of the rotating vanes, a nozzle having a passage which expands from the throat to the discharge end, and a conduit receiving fluid from the discharge end of the nozzle.

6. In a centrifugal compressor, the combination of a caslng, a rotating element mounted therein, blades for the rotating element which are curved at the ends in the direction of rotation, and vanes or blades for directing the fluid entering the rotating element, the said blades being curved at the ends in a direction opposite to those of the rotating element.

7. In a centrifugal compressor, the combination of an impeller having blades passage of shaped to simultaneously impart velocity to the fluid and, compress it,an annular nozzle which surrounds the peripheral ends of the blades and receives the fluid therefrom, the said nozzle having diverging side walls and straight sided tangential partitions to form passages each witha restricted inlet and an enlarged outlet, the length of the passage being considerably greater than the width at any pointvmeasured in a plane perpendicular to the direction of flow of the fluid so that the fluid will be compressed in the passage, will have its velocity reduced to a predetermined small amount and its temperature increased, a casing for the nozzle and impeller, and an inlet and an outlet.

8..I n a centrifugal compressor, the combination of a caslng, a rotating impeller mounted therein and having radially disposed vanes shaped to simultaneously imart velocity to an elastic fluid and compress it by centrifugal force and to discharge it peripherally with the velocity and reduced volume unimpaired into the nozzle, an annular nozzle that surrounds the impeller and receives thefluid directly from it, said nozzle having partitions extending in the general direction of rotation and in the plane of the impeller which form tangentially arran ed definite passages that receive fluid from the impeller, and are of properly varying cross-section in thedirection of their length to diminish the velocity of the fluid as received from the impeller and cause additional compression and dis- 7 fluid and retains it in its compressed state,

and a discharge conduit.

9. In a centrifugal compressor for elastic fluids,'.the combination of a casing, a rotating impeller mountedtherein having vanes with passages between them shaped to decrease the velocity of the elastic fluid relative to the impeller and cause compression of the fluid in addition to the compression caused by the centrifugal action of the said impeller, an annular nozzle that surrounds the impeller in the plane thereof, and hasa properly varying cross-section 1n the direction of the stream lines, said nozzle receiving and directing the fluid, dimlnishing its velocity and causlng addltional compression and discharging it with a'relatlvely low residual velocity, a conduit receiving the fluidfrom the nozzle, and a second conduit which supplies the, fluid to the inlet ends of the impeller vanes.

10. In a centrifugal compression for elastic fluids, the combination of a casing, a rotating impeller mounted therein and having vanes for compressing and impart-- ing velocity to the elastic fluid, said-vanes receiving fluid at their inner ends and discharging it outwardly, a driving shaft for the impeller, an annular nozzle into Which the impeller discharges which has a passage of properly varying cross-section in the direction of the stream lines with its largest cross-section at the point of final discharge, said nozzle receiving, guiding and directing the elastic fluid from the impeller and also compressing and discharging it with relatively low residual velocity, and means for conveying elastic fluid to the inlet ends of the vanes.

11. In a compressor for elastic fluids, the combination of a casing, a rotating impeller mounted therein and having vanes for compressing and imparting velocity to the elastic fluid, a driving shaft for the impeller,

an annular nozzle into which the impeller discharges throughout its entire circumference, said nozzle having a passage which is wholly divergent in the direction of the stream lines With its largest cross-section at the point of final discharge, and receiving, guiding and directing the elasticfluid received from the impeller and also compressing and discharging it with relatively low residual velocity, and means admitting elastic fluid to the inlet ends of the vanes. In witness whereof I have hereunto set my hand this seventh day of December, 1904. SANFORD A. MOSS."

Witnesses:

JOHN A. MoMAnUs, Jr., DUGALD MoK. MCKILLOP. 

